Chloride corrosion of reinforcing steel

Introduction. Many years of experience in examining corrosion conditions show the dangerous adverse effects of chloride media on reinforced concrete structures.

Although a large number of domestic and foreign publications have been devoted to the aggressive action of chloride salts on reinforcing steel, protection against chloride corrosion remains a relevant issue.

Aim. In this work, the state of this problem, along with the methods for determining the chloride content in concrete, was assessed in order to propose the means to increase its protective action in aggressive chloride media.

Materials and methods. This article discusses the following issues:

– maximum permissible chloride content in concrete;

– binding of chlorides by components in the matrix, the role of the mineral composition of cement;

– critical evaluation of methods for determining the chloride content in concrete;

– reduction of the diffusion permeability of chlorides in concrete as a method of corrosion protection.

Results. The article presents the data on moisture tests of reinforced concrete prepared using Portland cement having various contents of alite, belite, and tricalcium aluminate, as well as CaCl₂ additive.

Indicated were the challenges of identifying aggressive free chlorides in the matrix. The need to develop a standard method for determining free chlorides in concrete was discussed. Until such a standard is developed, the chloride aggressiveness to steel in concrete can be assessed by the electrochemical method. It was shown that concretes of extremely low diffusion permeability obtained using advanced complex additives that reduce the water demand of concrete mixtures and change the charge of the matrix surface can be used as a protection measure against chloride corrosion.

Presented are the results of determining the potentials of steel in concrete by electrochemical method, chlorides in concrete by colorimetric method, and diffusion permeability of chlorides in concrete.

Conclusion. The corrosion activity of chlorides against reinforcing steel depends on a large number of factors, including the total chloride content and the amount of free, physically, and chemically bound chlorides.

Since chloride binding depends on a large number of technological factors, it is recommended to perform electrochemical tests of reinforcing steel in concrete as per GOST 31383 to assess the hazard level of chlorides introduced into concrete with initial materials; a decision on the protective measures for reinforcing steel in chloride environments should be made on the basis of the obtained results.

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